Overcharging

[Donheist]

20 minutes from port under motor we smelled overheating batteries - checked and 17v going to engine battery and service batteries. Back off the revs and volts drop to something acceptable. We limped into port.

My diagnosis is duff alternator and ordered another one on the way in which will be here in a few days - not expensive, can’t hurt to have spare.

But Calder and other places suggest I should also check battery and regulator. And my usually very wise Marina folk are suggesting I get an electrician “are you SURE it’s the alternator?”

Views?

Would you do any other checks or is it open and shut?

System deets -

engine battery new, 2 x 230ah service batteries 2 years old.

200w solar plus duogen to service only via mppt

65a victron and Alternator goes to split charge diode. Also have a battery to battery saver to keep engine battery trickled up over winter

Have emergency parallel, between two and battery monitor in the engine, smart shunt on service.

 

[Boater Sam]

Presume that the charge voltage is only regulated by the alternator then it must be faulty.

Presuming that you may have a separate alternator controller- regulator then it could have lost its sensing connection to your batteries allow in it to go to maximum charge. Check on that wire if this is the case.

 

[bignick]

What sort of alternator and battery regulator do you have?

I have a Merlin Alternator Management System (AMS) fitted on my boat, which I thought was faulty. It may still be, but it will be a pain to remove completely. The AMS increases the charging voltage above that output by the alternator, I read in the manual that if you disconnect the ‘voltage sense’ wire between the AMS and the battery then the AMS is effectively disabled. I did this and the charging voltage returned back to its original level of 14.3V and the output is managed by the alternator itself. It would be worth reading the manual for your external regulator to see if you can do the same? It proved to be a good way to troubleshoot the problems I was having.

Also, many years ago I had a Rover 620Ti, which liked to cook its alternator diodes. The symptom would be that the wipers would go faster when you revved the engine. On checking, the output voltage increased with engine revs and it was discovered that the alternator diodes had failed. Sounds very similar to what you are experiencing.

 

[ash2020]

Sounds like you know at least as much as your average electrician. I've always been a proponent of that old saying, "if you want a job doing well, do it yourself". I'm sure you'll handle it. Good luck.

 

[Alex_Blackwood]

Presume that the charge voltage is only regulated by the alternator then it must be faulty.

Presuming that you may have a separate alternator controller- regulator then it could have lost its sensing connection to your batteries allow in it to go to maximum charge. Check on that wire if this is the case.

That could be the case with an internal alternator regulator as well. However, in that case, I would still expect the voltage to be regulated to the alternator design level.

 

[Bristolfashion]

Sounds like you know at least as much as your average electrician. I've always been a proponent of that old saying, "if you want a job doing well, do it yourself". I'm sure you'll handle it. Good luck.

I'll remember that for the vasectomy!

 

[Donheist]

So checked batteries under load - cranked engine 10s and stayed north of 10v so battery not terminal. Checked all wiring from alternator to split charge diode and batteries. Looks solid. So conclusion: alternator. Right?

So I warm up the engine for my oil change and with revs in neutral and and then also tried under load, my engine battery voltage peaked at 13.7. Only difference is that service batteries are depleted a bit.

So cannot manifest my 17v again. I will charge both batteries overnight and then run engine on fully charged batteries and see what happens.

 

[bignick]

I’m not sure how you’re monitoring battery charging voltage, but it’s worth doing it with a multimeter direct to the battery terminals. I’ve found that I can see some very strange results on the voltmeter on the panel if someone has plugged a phone charger or similar into the cigarette lighter socket.

 

[William_H]

Sounds fairly simply it is a failed alternator regulator. This may be built in to alternator (under 2 screws at the back) or a remote (smart) regulator (so check sensing wire to battery). Regulator failure is not uncommon. My son had same on a Toyota Camry damaged a fair bit of electrics. Also saw it on a twin engined Cessna with a lot of electrical damage resulting. Regulator transistor often goes short circuit internal failure resulting in max field current to alternator so full output in to batteries. ol'will

 

[noelex]

Sounds fairly simply it is a failed alternator regulator. This may be built in to alternator (under 2 screws at the back) or a remote (smart) regulator (so check sensing wire to battery). Regulator failure is not uncommon.

As the post above states, 17V indicates a faulty alternator regulator. The batteries may be toast by this stage.

A simple solution is to install an external alternator regulator. This will have better performance than the internal regulator, even before it failed.

 

[Alex_Blackwood]

So checked batteries under load - cranked engine 10s and stayed north of 10v so battery not terminal. Checked all wiring from alternator to split charge diode and batteries. Looks solid. So conclusion: alternator. Right?

So I warm up the engine for my oil change and with revs in neutral and and then also tried under load, my engine battery voltage peaked at 13.7. Only difference is that service batteries are depleted a bit.

So cannot manifest my 17v again. I will charge both batteries overnight and then run engine on fully charged batteries and see what happens.

From the above I would suggest that you have, or have had, a "Bad" connection somewhere that you have rectified, either permanently, or temporarily
Possibly your alternator is OK. Won't hurt to remove it and have it checked out if you have an auto electrical repair facility handy. If not I would suggest monitoring your charging voltages and see how you go. https://www.google.com/search?
PS. it is obvious that some of the posters do not read the thread before bursting into print

 

[Donheist]

From the above I would suggest that you have, or have had, a "Bad" connection somewhere that you have rectified, either permanently, or temporarily
Possibly your alternator is OK. Won't hurt to remove it and have it checked out if you have an auto electrical repair facility handy. If not I would suggest monitoring your charging voltages and see how you go. https://www.google.com/search?
PS. it is obvious that some of the posters do not read the thread before bursting into print

Thank you - good suggestion. I could swap the new one in and get the current one looked at at leisure. Pa thank you for the link - reminds me I need to change location. We are in Alghero now

 

[B27]

It seems unusual these days to have diode splitter and not also have some external alternator regulator to compensate for its diode drop.

It is vaguely plausible that some alternators will generate excess volts if not connected to a functioning battery, so maybe it's possible that something else destroyed the batteries, or there is a loose connection etc etc

But obviously, the system was sound enough to start the engine, so at least one battery must have been OK.

All you can do is check everything, including the things you trust and particularly the wiring diagram.

Alternators are quite tough old things, so 'are you sure it's the alternator?' is generally fair comment IMHO.
But if it's been modded or boosted in some way to work with the diode splitter, who knows?

Also, check grounds and isolate other charging sources to test the alternator.
And remember Alternators are AC animals at heart, measuring DC levels is not the whole story.
Some cheap meters read rubbish when presented with a messy AC + DC signal.

 

[Donheist]

It seems unusual these days to have diode splitter and not also have some external alternator regulator to compensate for its diode drop.

It is vaguely plausible that some alternators will generate excess volts if not connected to a functioning battery, so maybe it's possible that something else destroyed the batteries, or there is a loose connection etc etc

But obviously, the system was sound enough to start the engine, so at least one battery must have been OK.

All you can do is check everything, including the things you trust and particularly the wiring diagram.

Alternators are quite tough old things, so 'are you sure it's the alternator?' is generally fair comment IMHO.
But if it's been modded or boosted in some way to work with the diode splitter, who knows?

Also, check grounds and isolate other charging sources to test the alternator.
And remember Alternators are AC animals at heart, measuring DC levels is not the whole story.
Some cheap meters read rubbish when presented with a messy AC + DC signal.

Hmm. We
Stripped out a lot of complexity introduced by the previous owner (2 alternators, inverter, 2 shore power chargers, regulator)….

But I am open to looking again at the system now. I could switch out the diode for a regulator. Any recommendations?

 

[PaulRainbow]

Hmm. We
Stripped out a lot of complexity introduced by the previous owner (2 alternators, inverter, 2 shore power chargers, regulator)….

But I am open to looking again at the system now. I could switch out the diode for a regulator. Any recommendations?

A Victron Argofet.

 

[Donheist]

A Victron Argofet.

Ordered. Thank you